These studies represent a continuation of our long term interest in the relationship of metabolism to transport events in intact human erythrocytes. In this study, the free ATP and DPG concentrations in cold-stored human erythrocytes will be determined by ultrafiltration of lysates prepared by a French pressure device. P31 nuclear magnetic resonance spectroscopy will be employed to follow the changes in free ATP and DPG concentrations in intact erythrocytes as a function of the period of cold storage. ATP and DPG binding in intact erythrocytes will also be determined by P31 NMR spectroscopy under physiological conditions, i.e. at pH 7.4 and 37 degrees, by comparing the NMR signals obtained with those of a model hemoglobin solution in which the DPG, ATP, and Mg ions concentrations are arranged to simulate those in the intact cell. In addition, the role of Mg ions on ATP and DPG binding will be systematically examined in model hemoglobin solutions at 37 degrees and 5 degrees, since differences in AtP binding at the two temperatures may explain the differences in free ATP concentrations at the two temperatures. Subsequent work will be directed to the study of the relationship of free ATP concentration to active Na extrusion from the intact red cell. BIBLIOGRAPHIC REFERENCES: Marshall, W.E., L.S. Greenwald, J.M. Goldinger and A. Omachi. The influence of deoxygenation on human erythrocyte metabolism. Fed. Proc. 34: 355, 1975. Costello, A.J.R., W.E. Marshall, A. Omachi and T.O. Henderson. P31 NMR studies of adenosine triphosphate and 2,3-diphosphoglyceric acid interactions with hemoglobin. Fed. Proc. 34: 603, 1975.